User:Tilman Schirmer/Sandbox 110

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Repetitive torsion angles


A polypeptide chain with a repetition of identical phi-psi torsion angles yields a helical structure.

phi-psi = (180o, 180o), fully extended chain: model ,  Calpha-trace. Note the unfavorably close distance between the carbonyl oxygen and the Cβ-atom of the next residue.

phi-psi = (-110o, 130o), extended chain: cartoon , main-chain , Calpha-trace ; this is the β-strand conformation found in beta-sheets

Note:

 polypeptide forms a zig-zag with side-chains protruding towards alternating (up, down) directions

 the polypeptide main-chain is right-twisted as can been seen when looking along the chain

 the side-chains point towards alternate directions

Also strands with a left-twist are allowed, but they occur less frequent. This strand has phi-psi values of (-140o, 130o). See also Ramachandran Plots, http://en.wikipedia.org/wiki/Ramachandran_plot.

phi-psi = (70o, 180o): model , Calpha-trace ; note that there are clashes (where?)

phi-psi = (-60o, -40o), α-helix: <scene name='User:Tilman_Schirmer/Sandbox_100/Helix/1'>model , <scene name='User:Tilman_Schirmer/Sandbox_100/Helix/2'>Calpha-trace

phi-psi = (-50o, -26o), 310 helix: <scene name='User:Tilman_Schirmer/Sandbox_100/310helix/1'>model , <scene name='User:Tilman_Schirmer/Sandbox_100/310helix/2'>Calpha-trace